超穎透鏡頻域式光學同調斷層內視鏡之設計與開發

Design and Development of Metalens-based Spectral Domain Optical Coherence Tomography Endoscope

洪誠(Cheng Hung)

指導教授 ： 黃光裕 ； 駱遠

國立臺灣大學/工學院/機械工程學系/碩士(2024年)

https://doi.org/10.6342/NTU202402712

摘要

光學同調斷層掃描術(Optical Coherence Tomography, OCT)是一種用於獲取組織高解析度斷層影像的無侵入式成像技術。然而，傳統使用的內驅動式梯度折射率透鏡 (GRIN lens) OCT內視鏡受限於透鏡性能，在成像性上難以兼顧。本研究旨在設計開發一種基於超穎透鏡(Metalens)的OCT內視鏡，以期突破這一技術瓶頸。本文首先對OCT系統的基本原理進行了介紹，並通過理論計算了頻域式OCT的光學元件規格的最佳化配置。在訊號處理方法中，採用了k線性化修正以及色散補償提升了成像解析度。另外，也提出了基於超穎透鏡的OCT內視鏡設計方案。本研究針對OCT常用的近紅外波段設計了一款NA=0.5的超穎透鏡，通過對奈米結構的調控以及CST模擬軟體的驗證，在直徑3 mm、焦距3 mm的尺寸下實現了良好的聚焦性能。在此基礎上，分別針對基於傳統GRIN透鏡 (NA = 0.46) 和超穎透鏡 (NA = 0.5) 的OCT內視鏡原型，通過一系列性能測試和成像實驗進行了評估。與GRIN透鏡相比，超穎透鏡OCT內視鏡的縱向解析度從13.75 μm提高到9.14 μm；動態範圍從2 mm擴展到2.7 mm，並分別可拍攝到四片以及五片的蓋玻片。超穎透鏡的優異聚焦特性使其在OCT成像中展現出更清晰的精細結構和層間界面。最後，本研究也設計了微小型圓周徑向掃描裝置。該裝置採用外驅動式壓電致動器設計，避免了內驅動設計所產生的電線遮擋問題，提高了拍攝影像的穩定性。並在驗證了縱向以及橫向解析能力，可成功量測到六片蓋玻片以及解析度測試片之4-6組線對。也測試了Meta-OCT內視鏡之生物影像成像能力，並成功拍攝出洋蔥、洋蔥表皮、葉片組織之圓周縱向剖面影像以及豬皮線剖面影像。因此，經由本研究可得知超穎透鏡在提升OCT內視鏡成像性能方面具有一定的潛力，為提升OCT內視鏡的成像性能嘗試提供了一種新的解決方案。

關鍵字

頻域式光學同調斷層掃描術 ； 內視鏡 ； 梯度折射率透鏡 ； 超穎透鏡 ； 圓周掃描

並列摘要

Optical Coherence Tomography (OCT) is a non-invasive imaging technique used to obtain high-resolution cross-sectional images of tissues. However, traditional internally driven GRIN (Gradient Refractive Index) lens OCT endoscopes are limited by lens performance, making it difficult to balance imaging quality. This study aims to design and develop a metalens-based OCT endoscope to overcome this technical bottleneck.
This research first introduces the basic principles of the OCT system and optimizes the optical component specifications of frequency-domain OCT through theoretical calculations. The signal processing methods include k-linearization correction and dispersion compensation to enhance imaging resolution. Additionally, a design scheme for a metalens-based OCT endoscope is proposed. This study designs a metalens with an NA (Numerical Aperture) of 0.5 for the near-infrared band commonly used in OCT. By controlling nanostructures and verifying with CST simulation software, good focusing performance is achieved with a diameter of 3 mm and a focal length of 3 mm.
Based on this, prototypes of OCT endoscopes based on traditional GRIN lens (NA = 0.46) and metalens (NA = 0.5) were designed. Performance tests and imaging experiments were conducted to evaluate the two types of OCT endoscopes. Compared to the GRIN lens, the metalens OCT endoscope's longitudinal resolution improved from 13.75 μm to 9.14 μm; the dynamic range expanded from 2 mm to 2.7 mm, allowing the imaging of four and five cover glasses, respectively. The superior focusing characteristics of the metalens enabled it to exhibit clearer fine structures and interlayer interfaces in OCT imaging.
Finally, this study also designed a miniature circumferential radial scanning device using an external drive piezoelectric actuator to avoid the wire obstruction problem caused by internal drive design, thereby improving imaging stability. It verified the longitudinal and transverse resolution capabilities, successfully measuring six cover glasses and resolving lines 4-6 in the resolution test pattern. The biological imaging capability of the Meta-OCT endoscope was tested, successfully capturing circumferential cross-sectional images of onion, onion epidermis, and leaf tissues. Therefore, this study demonstrates the potential of metalens in enhancing OCT endoscope imaging performance, providing a new solution for improving OCT endoscope imaging capabilities.

並列關鍵字

Spectral-domain optical coherence tomography ； Endoscope ； Gradient refractive index lens ； Metalens ； Circumferential scanning

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